1. Field of the Art
The present invention relates to a bearing lubricating structure for rotary machinery. More particularly, the present invention relates to a bearing lubricating structure for rotary machinery which is suitable for built-in lubrication type positive-displacement compressors, turbocompressors, vacuum pumps or the like.
2. Prior Art
The following are conventional methods of supplying a lubricating oil to a bearing of a rotary machine:
(1) When the peripheral speed of the bearing part is relatively low:
A method wherein a lubricating oil that is splashed by an oil disk and flows down on the inner wall surface of a cover of a bearing housing is supplied to the bearing through an oil supply passage provided in the bearing housing.
(2) When the peripheral speed of the bearing part is relatively high:
A method wherein forced lubrication (jet lubrication) is carried out by a gear pump. For example, see Japanese Patent Application Public Disclosure (KOKAI) No. 58-193997 (1983).
However, the above-described conventional methods (1) and (2) suffer from the following problems.
With the method (1), although the lubricating structure is simple, it is impossible to obtain a sufficiently high feed rate of lubricating oil. Accordingly, this method cannot be adopted for the bearing lubricating structure of a high-speed rotary machine. Further, with the method (1), the rotor shaft and the casing are exposed to a compressed high-temperature gas.
Although the casing is generally provided with a cooling jacket so that it can be cooled, the rotor shaft cannot be cooled and hence heats up to a high temperature. Accordingly, while the outer ring of a rolling bearing attached to the casing does not heat up to a high temperature, the inner ring that is attached to the shaft is heated to a high temperature. Therefore, there is a likelihood that the required bearing clearance will not be ensured and the bearing will burn out. In addition, if the feed rate of lubricating oil is low, a sufficient cooling effect cannot be obtained. Therefore, it is impossible to reduce the temperature difference between the inner and outer rings.
With the method (2), although it is possible to obtain a sufficiently high feed rate of lubricating oil, a gear pump and oil supply piping are needed. Accordingly, this method invites a rise in costs and lacks compactness and ease of use.